1. Field of the Invention
The present invention relates to a radio communication system and a transmission apparatus and a reception apparatus for use in this system, and in particular to a radio communication system of CDMA (code division multiple access) and a transmission apparatus and a reception apparatus for use in the system.
2. Description of the Related Art
Conventionally, in the CDMA method, a particular code is allocated for each channel and modulated waves of the same carrier frequency are spectrum-dispersed with this code, so that a reception side can recognize a desired channel by code synchronization.
Firstly, a conventional radio communication system will be explained with reference to FIG. 7 to FIG. 10.
The radio communication system is constituted by a repeating apparatus serving as a transmission apparatus 50 and a reception apparatus 60.
FIG. 8 shows a configuration of the repeating apparatus 50. An information item from the line is frame-divided and encoded by an encoder 51, after which a resultant signal is multiplied by a first diffusion code in a multiplier 52. The signal which has been multiplied by the first diffusion code is adjusted in a controller 53 so as to be a maximum gain, which is supplied to an adder 54. Here, the encoder 51 stores the output information in its internal storage. Moreover, the encoder 51 adds an error detection code (such as CRC) to each of the frames before output. The adder 54 performs an addition of signals from a plurality of channels. A resultant signal of this addition is transmitted via a transmitter 55 from an antenna 56.
FIG. 9 shows a configuration of the reception apparatus 60. A signal received via an antenna 61 by a receiver 62 is multiplied by a first diffusion code in a multiplier 63 and decoded in a decoder 64, and then processed by a data terminator 65. Here, in the decoder 64, the error detection code added to the received information is checked. If an error is detected, the error information is added to the reception information, which is supplied to an encoder 66 without passing through the data terminator. This retransmission request indicating a code error is coded by the encoder 66 and multiplied by a second diffusion code, after which the request is transmitted via a transmitter 68 from the antenna 61. Moreover, a transmission information generated from the data terminator 65 is also transmitted from the antenna 61 via the encoder 66, the multiplier 67, and the transmitter 68.
Referring again to FIG. 8, explanation will be continued. The retransmission request and other information transmitted from the reception apparatus 60 are received by the repeating apparatus 50. A signal which has reached the antenna 56 is fetched by the receiver 57 and multiplied by a second diffusion code by the multiplier 58 before decoded by the decoder 59. If it is found in the decoding that the reception information contains a bit indicating the code error of the information transmitted, the decoder 59 makes a retransmission request to the encoder 51. Upon reception of the retransmission request, the encoder 51 retransmits using the first diffusion code the frame which has been retained in the storage. Upon reception of the retransmitted frame, the reception apparatus 60 performs a check whether a code error is contained. If no error is contained, the frame is supplied to the data terminator 65. The data terminator 65 processes frames in the order of the frame number.
For example, as shown in FIG. 10, if a code error has occurred in transmission of frame No. 1, a frame indicating a retransmission request is returned from the reception apparatus, during which a frame No. 2 is transmitted from the repeater apparatus 50. At this point of time, the repeater apparatus 50 which has received the retransmission request for the frame No. 1 interrupts transmission of frame No. 3 and transmits the frame No. 1. After this, transmission of the frame No. 3 and after is continued. In the reception apparatus 60, information is processed in the order of the frame number. This assures reliability of the communication between the repeater apparatus 50 and the reception apparatus 60.
However, in the aforementioned conventional example, in the repeater apparatus, the same channel, i.e., the sample diffusion code is used for the normal transmission and the retransmission and accordingly, during the retransmission, the normal transmission operation should be interrupted. This lowers the transmission capacity (throughput). This problem is serious in the CDMA method which has originally a lower transmission capacity compared to the FDMA and TDMA.
It is therefore an object of the present invention to provide a radio communication system not causing a transmission capacity lowering even when retransmitting a frame which has caused in the CDMA method, as well as a transmission apparatus and a reception apparatus used in this system.
The radio communication according to the present invention comprises a transmission apparatus and a reception apparatus. The transmission apparatus includes: an encoder for encoding an information to be transmitted and adding an error detection code; a storage for storing a signal to be output from the encoder; a transmission channel for transmitting the information which has been encoded by the encoder so as to be transmitted; a first multiplier provided in the transmission channel, for multiplying an output signal from the encoder by a first diffusion code so as to be a transmission signal destined to the reception apparatus; a second multiplier for multiplying a signal received from the reception apparatus, by a second diffusion code; a decoder for decoding the output signal from the second multiplier; and a transmission/reception block for transmitting and receiving a signal to/from the reception apparatus. On the other hand, the reception apparatus includes: a first multiplier for multiplying a reception signal from the transmission apparatus, by the first diffusion code; a decoder for decoding an output signal from the first multiplier and checking whether the reception signal contains a code error according to the error detection code; an encoder for encoding a retransmission request identifying a frame number which has caused a code error if any detected by the decoder; a second multiplier for multiplying an output signal from the encoder, by the second diffusion code, so as to be a transmission signal destined to the transmission apparatus; and a transmission/reception block for transmitting and receiving a signal to/from the transmission apparatus.
Here, the decoder of the transmission apparatus has a function to instruct the encoder of the transmission apparatus, upon reception of a retransmission request from the reception apparatus, to retransmit the frame to be retransmitted. Moreover, the encoder of the transmission apparatus has a function, in response to the instruction of retransmission, to read out from the storage an information to be transmitted and a function to output the information to be retransmitted simultaneously with the information to be transmitted.
Furthermore, the transmission apparatus includes a retransmission channel for transmitting the information which has been read out from the storage by the encoder so as to be retransmitted, and a third multiplier provided in the retransmission channel, for multiplying an output signal from the encoder, by a third diffusion code so as to be a transmission signal destined to the reception apparatus. On the other hand, the reception apparatus further includes a third multiplier for multiplying a reception signal from the transmission apparatus, by the third diffusion code so as to be an input signal to the decoder of the reception apparatus.
In the radio communication system, it is preferable that the encoder of the transmission apparatus have a function for adding an error detection code to the information to be transmitted and outputting the information and that the decoder of the reception apparatus have a function to check whether a code error is present in the decoded information to be retransmitted.
According to another aspect of the present invention, there is provided a transmission apparatus for use in combination with a reception apparatus in a radio communication system, the transmission apparatus comprising: an encoder for encoding an information to be transmitted and adding an error detection code to the information encoded; a storage for storing a signal produced from the encoder; a transmission channel for transmitting the encoded information to be transmitted; a first multiplier provided in the transmission channel, for multiplying the output signal from the encoder by a first diffusion code so as to be transmission signal destined to the reception apparatus; a second multiplier for multiplying a signal received from the reception apparatus, by a second diffusion code; a decoder for decoding an output signal from the second multiplier; and a transmission/reception block for transmitting and receiving a signal to/from the reception apparatus.
Here the decoder has a function to instruct the encoder, upon reception of a retransmission request from the reception apparatus, to retransmit a frame requested to be retransmitted. Moreover, the encoder has a unction, in response to the instruction of retransmission, to read out from the storage an information to be transmitted and a function to output the information to be retransmitted simultaneously with the information to be transmitted.
The transmission apparatus further includes a retransmission channel for transmitting the information which has been read out from the storage by the encoder so as to be retransmitted, and a third multiplier provided in the retransmission channel, for multiplying an output signal from the encoder, by a third diffusion code so as to be a transmission signal destined to the reception apparatus.
In the transmission apparatus, it is preferable that the encoder have a function to add an error detection code to the information to be retransmitted, before outputting the information.
According to still another aspect of the present invention, there is provided a reception apparatus for use in combination with a reception apparatus in a radio communication system, the reception apparatus comprising: a first multiplier for multiplying a reception signal from the transmission apparatus by a first diffusion code; a decoder for decoding an output signal from the first multiplier and checking whether a code error is present in the reception signal according to an error detection code; an encoder for, upon detection of a code error in the decoder, encoding a retransmission request identifying a frame number which has caused the code error and outputting the retransmission request; a second multiplier for multiplying an output signal from the encoder by a second diffusion code so as to be transmission signal destined to the transmission apparatus; and a transmission/reception block for transmitting and receiving a signal to/from the transmission apparatus. Furthermore, the reception apparatus further comprises a third multiplier for multiplying the reception signal from the transmission apparatus by a third diffusion code so as to be an input signal to the decoder.
In the reception apparatus, it is preferable that the decoder have a function to check whether a code error is present in the decoded information to be retransmitted.